Resistance to Interference and Positive Symptomatology in Schizophrenia

Abstract

Resistance to disruption by visual distractors seems to be a robust finding in schizophrenic patients, especially those with positive symptoms. This seems to contradict the view that positive symptoms are linked to poor inhibition of distracting stimuli. To help decide between these opposing theories, we assessed the interference effect in the Stroop colour and word test, and its correlation with positive symptomatology in schizophrenic patients. Two hypotheses were pitted against each other: (1) that a positive correlation would be observed between interference and positive symptoms, suggesting that positive symptoms were linked to a deficit in inhibition of nonrelevant stimuli; and (2) that a negative correlation would be observed, suggesting that positive symptoms were linked to resistance to disruption by nonrelevant stimuli. A total 40 patients and 40 normal controls were administered the Stroop test and an index of interference was derived. The amount of interference was not significantly increased in patients. No positive correlation with symptoms was observed, invalidating the first hypothesis. A negative correlation was observed, however, between the amount of interference and the score of hallucinations. This confirmed the second hypothesis (i.e. more hallucinations being associated with more resistance to distractors). This is in agreement with studies showing that resistance to negative priming and latent inhibition was linked to positive symptomatology in schizotypes or schizophrenic patients. It is proposed that resistance to negative priming, to latent inhibition, and to interference in patients with positive symptomatology stem from incomplete processing of distractor information.